Various methods of measuring the complex permittivity of a dielectric material are known. Some methods use a waveguide, a coaxial line, or a resonant cavity loaded with the material to be tested. Another known method uses a waveguide radiating into the material to be tested.
In some cases, it is necessary to measure electromagnetic characteristics on materials raised to very high temperature, i.e. to more than 1000.degree. C. This applies, in particular, to dielectric materials which are heated to a large extent in use, e.g. the materials used for the outside portions of aircraft or other air or space vehicles.
The known methods are unsuitable when measurements need to be performed on a material raised to high temperature. Because of thermal deformation, this applies in particular to putting a waveguide into contact with the material to be tested. In addition, heat losses by contact with the waveguide prevent a uniform temperature being obtained within the material under test.
Thus, the object of the present invention is to provide an apparatus which is particularly suitable for measuring electromagnetic characteristics of a material at very high temperature.